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《Acta Geologica Sinica》 2006-12
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A Possible New HP/UHP(?) Metamorphic Belt in China: Discovery of Eclogite in the Lasha Terrane, Tibet

YANG Jingsui~ 1) , XU Zhiqin~ 1) , GENG Quanru~ 2) , LI Zhaoli~ 1) , XU Xiangzhen~ 1) , LI Tianfu~ 1) ,REN Yufeng~ 1) , LI Huaqi~ 1) , CAI Zhihui~ 1) , LIANG Fenghua~ 1) , CHEN Songyong~ 1) 1) Key Laboratory for Continental Dynamics, Institute of Geology, CAGS, Beijing,1000372) Chendu Institute of Geology and Mineral Resources, China Geology Survey, Chendu, 610082  
Eclogite was first discovered in the Lasha terrane, northeast to the Lasha City. The eclogite occurs as a 500~600 m thick belt, extending in EW for over 10 km. Most eclogites are massive, coarse-grained and fresh. Three types of eclogite have been recognized, which are rutile eclogite, quartz eclogite and phengite eclogite. The clinopyroxenes in eclogite are mainly omphacite with 16%~44% of jadeite (Jd) molecules. The end member molecules for garnets in eclogite are pyrope 16%~33%, almondite 40%~54%, and grossular 22%~31%. p-t calculation based on Grt-Omp-Phe and Grt-Omp mineral assemblages yielded 2.58 GPa and 635℃, and 2.67 GPa and 730℃, respectively for sample 06Y-334, and samples 06Y-345 and 06Y-336T yielded t mainly in the range of 680~780℃and 640~740℃. Since the phengites in these samples occur as retrogressive minerals, the peak metamorphic p for these rocks may be higher than the calculated values and enter the coesite stable field (p2.8 GPa). Polycrystal quartz as pseudomorphs of coesite in garnet or omphacite may provide a possibility for looking for UHP metamorphic evidence. The Lasha eclogite belt most likely represents a new HP/UHP(?) metamorphic belt in China.
【Fund】: 中国地质调查局基础地质调查项目(编号1212010610107、1212010610105);; 国家自然科学基金重大国际合作项目(编号40610098)资助的成果。
【CateGory Index】: P588.1
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